In a fairly recent paper we showed that (within the limits alluded to above) the famous Ehlers symmetry [1]}, [2]} can be shown to be an additional symmetry, even in the four-dimensional theory. In this letter, we ask a different question. Can any of the Poincaré generators be lifted to be local? We will find that the Hamiltonian can indeed be made local and we can identify it with the Bondi-van der Burg-Metzner-Sachs (BMS) group which is an infinite-dimensional enhancement of the Poincaré group. In the usual formulation, this arises as the asymptotic symmetry group at null infinity for asymptotically flat spacetimes [3]}, [4]}, [5]}. There has been a renewed interest in the study of asymptotic symmetries following a recent body of work [6]}, wherein these symmetries have been connected to soft theorems for gauge theories. Here we will show the symmetry as a symmetry in the bulk avoiding the usual sensitivity to the boundary conditions and gauge choices imposed on the fields. At spatial infinity, for instance, under the standard boundary conditions in the Hamiltonian formulation of gravity, only the Poincaré algebra could be canonically realized, not the BMS algebra [7]}. In a recent work, however, the BMS group was recovered at spatial infinity by suitably relaxing the boundary conditions, thereby, resolving a longstanding disparity between the asymptotic structure at spatial and null infinity [8]}, [9]}.
